What Is a Glomerular Filtration Rate (GFR)?

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The glomerular filtration rate, or GFR, is a measure of how well your kidneys are cleaning your blood -- taking out waste and extra water. An estimated GFR test (eGFR) can tell your doctor how much of a certain waste product called creatinine is in your blood.

The test gets its name from the parts of your kidney that filter waste out -- they’re called glomeruli.

Who Needs This Test?

Your doctor may do an eGFR test as part of a regular physical exam, or she might recommend it if you have signs of kidney problems. Those can include:

How the eGFR Test Works

Before your test, be sure to tell your doctor about any drugs, vitamins, or dietary supplements you take. He may tell you not to take certain medicines or eat certain foods beforehand.

For the test, a doctor or nurse will take a sample of your blood. Then they’ll send it to a lab to see how much creatinine is in it. To figure out your results, they’ll use a mathematical formula that’s based on the amount they find, along with your age, gender, and race.

In general, if the amount of protein in your urine is normal, an eGFR result below 60 mL/min/1.73 m² can be a sign of kidney disease. But your doctor will be able to give you more specific information about your result, taking all your health information into account.